A stable silylene in a reactive environment: Synthesis, reactivity, and silicon extrusion chemistry of a coordinatively unsaturated ruthenium silylene complex containing chloride and η3-P-C-P ligands

Article abstract of DOI:10.1021/om0101801

Reaction of [(dcypb)ClRu(μ-Cl)₃Ru(dcypb)(N₂)] (1) with 4 equiv of the stable silylene 1,3-di-tert-butyl-l,3,2-diazasilol-2-ylidene (SiL₂^N) yields coordinatively unsaturated RuCl(η³-dcypb)(SiL₂

Full text of DOI:10.1021/om0101801

534
Organometallics 2002, 21, 534-540
A Sta ble Silylen e in a Rea ctive En vir on m en t: Syn th esis,
Rea ctivity, a n d Silicon Extr u sion Ch em istr y of a
Coor d in a tively Un sa tu r a ted Ru th en iu m Silylen e
Com p lex Con ta in in g Ch lor id e a n d η3-P -C-P Liga n d s
Dino Amoroso,† Michael Haaf,§,‡ Glenn P. A. Yap,† Robert West,§ and
Deryn E. Fogg*,†
Center for Catalysis Innovation and Research, Department of Chemistry, University of Ottawa,
Ottawa, Ontario, Canada K1N 6N5, and Organosilicon Research Center, Department of
Chemistry, University of Wisconsin, Madison, Wisconsin 53706
Received March 7, 2001
Reaction of [(dcypb)ClRu(µ-Cl)3Ru(dcypb)(N2)] (1) with 4 equiv of the stable silylene 1,3-
di-tert-butyl-1,3,2-diazasilol-2-ylidene (SiLN2) yields coordinatively unsaturated RuCl(η3-
dcypb)(SiLN2) (2). Complex 2 is a rare example of a trans-spanning diphosphine complex,
this geometry resulting from an unprecedented attack of the metal on the tetramethylene
ligand backbone. X-ray and solid-state 31P NMR and IR analysis reveal an agostic interaction
between the metal and a silylene But group. In solution, this interaction is observed only at
low temperature. Reaction of 2 with H2 containing trace H2O yields siloxane dimer [LN2Si-
(H)]2O 3 and the ruthenium hydride-H2 adduct [(dcypb)(H)Ru(µ-Cl)2(µ-H)Ru(dcypb)(H2)]
(4). Attempts to isolate 4 resulted in serendipitous crystallization of decomposition product
5, [(dcypb)(H)Ru(µ-Cl)3Ru(dcypb)(N2)]. X-ray analysis of 5 revealed a structure closely
analogous to that of 4, in which bridging hydride is replaced by chloride, and η2-H2 by η2-
N2. Displacement of silylene from 2 is facile: treatment with 1 atm of CO affords free SiLN
accompanied by RuCl(η3-dcypb)(CO)2 as a mixture of three isomers (6-8).
,
2
In tr od u ction
including by 1,2-migration from silyl hydrides.11 Par-
ticularly well developed is the coordination chemistry1-4,6
of 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene (SiLN2), the
first isolated example of a stable silylene, reported by
Denk and West in 1994.12 This compound can be
recognized as a silicon analogue of the stable N-
heterocyclic carbene ligands (“Arduengo carbenes”),13
which have recently attained a high profile in Ru-
catalyzed metathesis reactions. Irrespective of instal-
lation route, the stability of the bound silylene is
typically ensured by use of “innocent” ligands, nonco-
ordinating anions, and a coordinatively saturated metal.
With few exceptions,3,5,14 common catalytically relevant
ligands such as chloride, hydride, or phosphine have
been neglected. In the course of studies directed at the
design of novel ruthenium metathesis catalysts,15,16 we
developed facile routes to chlororuthenium complexes
containing the electron-rich chelating phosphine
Transition-metal derivatives of silylenes are of intense
interest for their potential relevance to a range of
organosilicon transformations, and development of routes
to such complexes has provided a rich area of inquiry.
Synthetic strategies focus on reactions of coordinatively
unsaturated precursors with a stable silylene1-6 or
generation and installation of the silylene in situ,7-10
* Corresponding author. E-mail: dfogg@science.uottawa.ca. Fax:
(613) 562-5170.
† University of Ottawa.
§ University of Wisconsin.
‡ Present address: Department of Chemistry and Biochemistry,
Elizabethtown College, One Alpha Drive, Elizabethtown, PA 17022.
(1) (a) Haaf, M.; Schmedake, T. A.; West, R. Acc. Chem. Res. 2000,
33, 704. (b) Schmedake, T. A.; Haaf, M.; Paradise, B. J .; Millevolte, A.
J .; Powell, D. R.; West, R. J . Organomet. Chem. 2001, 636, 17.
(2) Schmedake, T. A.; Haaf, M.; Paradise, B. J .; Powell, D.; West,
R. Organometallics 2000, 19, 3263.
(3) Dysard, J . M.; Tilley, T. D. Organometallics 2000, 19, 4726.
(4) Denk, M.; Hayashi, R. K.; West, R. J . Chem. Soc., Chem.
Commun. 1994, 33.
(5) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Maciejewski, H.
Organometallics 1998, 17, 5599.
(6) Petri, S. H. A.; Eikenberg, D.; Neumann, B.; Stammler, H. G.;
J utzi, P. Organometallics 1999, 18, 2615.
(7) (a) Tilley, T. D. The Chemistry of Organic-Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Vol. 2, Chapter
24, p 1415. (b) Tilley, T. D. The Silicon-Heteroatom Bond; Patai, S.,
Rappoport, Z., Eds.; Wiley: New York, 1991; Chapters 9 and 10, pp
245 and 309.
(8) (a) Wanandi, P. W.; Glaser, P. B.; Tilley, T. D. J . Am. Chem.
Soc. 2000, 122, 972. (b) Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.;
Rheingold, A. L. J . Am. Chem. Soc. 1994, 116, 5495. (c) Grumbine, S.
D.; Tilley, T. D. J . Am. Chem. Soc. 1993, 115, 7884. (d) Straus, D. A.;
Tilley, T. D. J . Am. Chem. Soc. 1987, 109, 5872.
(9) Straus, D. A.; Grumbine, S. D.; Tilley, T. D. J . Am. Chem. Soc.
1990, 112, 7801.
(10) Grumbine, S. K.; Mitchell, G. P.; Straus, D. A.; Tilley, T. D.;
Rheingold, A. L. Organometallics 1998, 17, 5607.
(11) Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed. Engl. 1998,
37, 2524.
(12) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.;
Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J . Am. Chem. Soc.
1994, 116, 2691.
(13) Arduengo, A. J .; Dias, H. V. R.; Harlow, R. L.; Kline, M. J . Am.
Chem. Soc. 1992, 114, 5530.
(14) J utzi, P.; Mohrke, A. Angew. Chem., Int. Ed. Engl. 1990, 29,
893.
(15) Amoroso, D.; Fogg, D. E. Can. J . Chem. 2001, 79, 958.
(16) Amoroso, D.; Fogg, D. E. Macromolecules 2000, 33, 2815.
10.1021/om0101801 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/10/2002

Ruthenium Silylene Complex
Organometallics, Vol. 21, No. 3, 2002 535
C6D6): 65.1 (br s), 52.2 (br s), ratio 1:1. 1H NMR (δ, C6D6):
5.95 (s, SiH), 5.80 (s, olefinic), 0.6-3.0 (m, aliphatic, 3, 4),
-13.8 (br s, RuH,Ru(H2), 4).
Rea ction of 2 w ith D2. Deuterium gas was bubbled
through a solution of 2 (10 mg, 12.8 µmol) in C6H6 (1 mL) in
a Teflon-lined screw-cap NMR tube (2 min). The sealed tube
was warmed at 50 °C for 24 h under D2. 2H NMR (δ, C6H6):
5.95 (s, SiD), 0.5-3.0 (br m, aliphatic, 4-d ), -13.8 (br s, RuD,
Ru(D2), 4-d ). 31P NMR (δ, C6H6): 65.1 (br s), 52.2 (br s); ratio
1:1.
dcypb (dcypb ) bis(dicyclohexyl)-1,4-phosphinobutane,
Cy2P(CH2)4PCy2), which displays a rich coordination
chemistry.15 We were thus interested in examining the
properties of the SiLN2 ligand within this coordinatively
unsaturated metal environment.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were carried out under
N2 using standard Schlenk or drybox techniques, unless
otherwise noted. Hydrogen (Praxair UHP Grade) and deute-
rium (Aldrich 99.8%) were purified by passage through a Deoxo
cartridge and an indicating Drierite column in series. CO
(Praxair) was passed through Drierite only. Dry, oxygen-free
solvents were obtained using an Anhydrous Engineering
solvent purification system and stored over Linde 4 Å molec-
ular sieves. C6D6 and toluene-d8 were dried over activated
sieves (Linde 4 Å) and degassed by consecutive freeze/pump/
thaw cycles. Ru2Cl4(dcypb)2(N2) (1) was prepared as previously
described.15 1H NMR (200 or 500 MHz) spectra were recorded
on a Varian Gemini 200 or Bruker AMX-500 spectrometer.
Solution 31P NMR (121 MHz), 13C NMR (75 MHz), and 29Si
NMR (58 MHz) spectra were recorded on a Varian XL-300
MHz spectrometer; solid-state NMR spectra, on a Bruker ASX-
200 MHz spectrometer (81 MHz for 31P). All 2D experiments
were carried out on the AMX-500 instrument. IR spectra were
measured on a Bomem MB100 IR spectrometer. Microana-
lytical data were obtained using a Perkin-Elmer Series II
CHNS/O instrument. Computational results were obtained
using the Cerius2-DMol3 molecular modeling suite from Mo-
lecular Simulations Inc.17 Density functional theory (DFT)
calculations were carried out with a Double Numerical basis
set and Perdew-Wang local correlation using the default grid.
Room -Tem p er a tu r e Rea ction of 2 w ith D2. Deuterium
gas was bubbled through a solution of 2 (10 mg, 12.8 µmol) in
C6H6 (1 mL) in a Teflon-lined screw-cap NMR tube (2 min).
The sealed tube was stored at RT under D2, and the reaction
monitored by 2H and 31P NMR. After 48 h signals for 4-d were
visible, accompanying those for 2. No incorporation of deute-
rium into the diphosphine backbone was observed prior to
formation of 4-d .
Rea ction of 2 w ith H2O. To a solution of 2 (10 mg, 12.8
µmol) in C6D6 (1 mL) under N2 in a Teflon-lined screw-cap
NMR tube was added degassed H2O (0.23 µL, 12.8 µmol). After
2 h at RT, <20% of 2 remained (1H, 31P NMR); several new
products were evident, of which only 15% of the integrated
intensity could be ascribed to 4. The tube was then purged
with H2. After 4 h, no 2 remained and the major product (50%
of integrated intensity) was 4. No further changes were
observed over 24 h.
Rea ction of 2 w ith H2O a n d H2. To a solution of 2 (10
mg, 12.8 µmol) in C6D6 (1 mL) in a Teflon-lined screw-cap NMR
tube was added degassed H2O (0.23 µL, 12.8 µmol). The sealed
tube was immediately purged with H2. Conversion to 4 and
siloxane 3 was complete within 6 h at RT (1H, 31P NMR.)
[(d cyp b)(H)Ru (µ-Cl)3Ru (d cyp b)(N2)] (5). Complex 5 was
serendipitously obtained on attempted isolation of 4 from the
reaction of 2 with H2. A benzene solution containing the
reaction products was reduced to an orange residue under
vacuum, washed with hexanes, and redissolved in benzene.
31P NMR analysis revealed the presence of many products,
including 4, characterized by resonances (many of which were
broad) between 87 and 2 ppm. 1H NMR, hydride region: δ
-19.5 to -20.6 (overlapping multiplets), -13.8 (br s, 4), -11
to -12 (two broad singlets). Small crystals of 5 deposited on
slow evaporation.
Ru Cl(η3-d cyp b)(SiLN2) (2). Reaction of 1 (0.198 g, 0.314
mmol Ru) with SiLN (0.127 g, 0.647 mmol) in C6H6 (10 mL)
2
at 50 °C gave a homogeneous deep red/brown solution over 4
h. Concentration and addition of cold hexanes afforded a yellow
precipitate, which was reprecipitated from benzene-hexanes.
1
Yield after drying under vacuum: 0.199 g (81%). H NMR (δ,
2
C6D6): 6.33 (d, olefinic, 1H, J HH ) 3.8 Hz), 6.17 (d, olefinic,
2
1H, J HH ) 3.8 Hz), 3.2-3.4 (m, aliphatic, 2H), 2.8-3.0 (m,
aliphatic, 2H), 1.0-2.7 (br m, aliphatic, 47H), 1.29 (s, But, 9H),
1.01 (s, But, 9H). 31P{1H} NMR (δ, C6D6): 60.2 (d, CH2CH2P,
2J PP ) 263 Hz), -10.3 (d, CHCH2P, 2J PP ) 263 Hz). Solid-state
31P NMR (80.9 MHz): 56.2 (d, CH2CH2P, 2J PP ) 267 Hz), -11.6
Rea ction of 2 w ith CO. A suspension of 2 (86 mg, 0.11
mmol) in 0.75 mL of toluene-d8 gave a homogeneous pale
yellow solution on stirring under 1 atm of CO. 1H NMR showed
complete loss of signals for bound silylene within 24 h and a
large singlet for free SiLN2. Three products evident by 31P NMR
were identified as isomeric Ru(η3-dcypb)(CO)2 species 6-8 (see
text). The high solubility of 6-8 in all solvents, including
hexanes, precluded separation from free silylene. 1H NMR (δ,
C6D6): 6.75 (s, olefinic, 2H), 0.8-3.4 (br, m, 51H), 1.40 (s, But,
2
(d, CHCH2P, J PP ) 267 Hz). 29Si{1H} NMR (δ, C6D6): 105.7
2
ppm (t, J PSi ) 32 Hz). IR (Nujol): ν(C-H) 2923, 2853, 2727,
2668 cm-1; (benzene): 2924, 2851 cm-1. The extreme air-
sensitivity of the complex resulted in fuming and immediate
decomposition to a dark brown powder on attempted combus-
tion analysis, giving data consistently low in carbon. Crystals
of 2 were obtained by slow evaporation of a benzene solution.
2
18H). 31P{1H} NMR (δ, C6D6): 77.6 (d, CH2CH2P, J PP ) 249
2
Hz, 6 or 7), 74.4 (d, CH2CH2P, J PP ) 246 Hz, 6 or 7), 72.9 (d,
Rea ction of 2 w ith H2. A solution of 2 (62 mg, 0.08 mmol)
2
2
CH2CH2P, J PP ) 164 Hz, 8), -29.0 (d, CHCH2P, J PP ) 249
in 5 mL of C6H6 was warmed at 50 °C for 24 h under H2.
2
Hz, 6 or 7), -29.9 (d, CHCH2P, J PP ) 246 Hz, 6 or 7), -38.2
Conversion of SiLN to siloxane dimer [LN2Si(H)]2O 3 was
(d, CHCH2P, 2J PP ) 164 Hz, 8). IR (Nujol, ν (CO), cm-1): 2010,
1925, 1880.
2
confirmed by detailed spectroscopic analysis (see text), rein-
forced by comparison with literature values.18 The inorganic
product is spectroscopically identical to Ru species Ru(dcypb)-
(H)(µ-Cl)2(µ-H)Ru(dcypb)(H2) 4, prepared by reaction of 1 with
potassium tri(sec-butyl)borohydride.19 Its isolation was thwarted
by decomposition problems, including dehydrogenation, as
indicated by the appearance of olefinic signals and a peak for
Rea ction of 2 w ith 13CO. The reaction was carried out as
above to afford the corresponding 13C isotopomers, 6′-8′. Peak
doubling in the 31P NMR spectrum due to 13C-31P coupling
confirms the presence of two carbonyl ligands in each molecule,
though second-order effects limit rigorous analysis of the 13C
NMR spectrum. 31P{1H} NMR (δ, C6D6): 77.6 (ddd, CH2CH2P,
1
dissolved H2 by H NMR (see text). Solution 31P{1H} NMR (δ,
2
2
2J PP ) 249 Hz, J PC ) 12 Hz, J PC ) 4.2 Hz, 6′ or 7′), 74.4
(ddd, CH2CH2P, 2J PP ) 246 Hz, 2J PC ) 11.6 Hz, 2J PC ) 4.6 Hz,
2
2
(17) Cerius2 Property Prediction; Molecular Simulations Inc.: San
Diego, 1999.
(18) Haaf, M.; Schmiedl, A.; Schmedake, T. A.; Powell, D. R.;
Millevolte, A. J .; Denk, M.; West, R. J . Am. Chem. Soc. 1998, 120,
12714.
6′ or 7′), 72.9 (dt, CH2CH2P, 8′, J PP ) 164 Hz, J PC ) 13.2
2 2
Hz), -29.0 (ddd, CH2CH2P, J PP ) 249 Hz, J PC ) 13.4 Hz,
2J PC ) 4.9 Hz, 6′ or 7′), -29.9 (ddd, CH2CH2P, J PP ) 246 Hz,
2
2
2J PC ) 11.5 Hz, J PC ) 3.6 Hz, 6′ or 7′), -38.2 (dt, CH2CH2P,
(19) Amoroso, D.; Fogg, D. E. Organometallics, submitted.
8′, 2J PP ) 164 Hz, 2J PC ) 13.4 Hz). 13C{1H} NMR (δ, C6D6; CO

536 Organometallics, Vol. 21, No. 3, 2002
Amoroso et al.
region only): 214.6 (m), 210.4 (m), 205.9 (m), 202.3 (m), 201.7
(m), 198.9 (m), 198.2 (m).
containing two phosphine ligands. The relatively small
coordination shift (cf. δ 78 for the free ligand) is in
keeping with values previously reported for complexes
of these stable silylenes.2-4,6 The characteristic singlet
at 6.75 ppm for the equivalent aromatic protons in free
Str u ctu r a l Deter m in a tion s of 2 a n d 5. Suitable crystals
were selected, mounted on thin glass fibers using paraffin oil,
and cooled to the data collection temperature. Data were
collected on a Bruker AX SMART 1k CCD diffractometer using
0.3° ω-scans at 0°, 90°, and 180° in φ. Unit-cell parameters
were determined from 60 data frames collected at different
sections of the Ewald sphere. Semiempirical absorption cor-
rections based on equivalent reflections were applied.20
Systematic absences in the diffraction data and unit-cell
parameters for 2 were consistent with space groups Pc (No.
7) and P2/ c (13). Only the solution in the acentric space group
option yielded chemically reasonable and computationally
stable results of refinement with a packing diagram that does
not display any overlooked crystal symmetry. A nil Flack
parameter indicates the true hand of the data set had been
determined. In analysis of 5, no symmetry higher than triclinic
was observed, and solution in the centrosymmetric option
yielded chemically reasonable and computationally stable
results of refinement. Both structures were solved by direct
methods, completed with difference Fourier syntheses, and
refined with full-matrix least-squares procedures based on F2.
Two symmetry-unique but chemically equivalent compound
molecules were located in the asymmetric unit of 2. One
cyclohexyl group in 2 displays distorted ellipsoids, suggesting
conformational disorder, but attempts to model the disorder
were unsatisfactory. A cocrystallized benzene molecule was
located in the asymmetric unit of 5. The hydride ligand in 5
could not be located and was ignored except in the calculation
of intrinsic properties. All non-hydrogen atoms were refined
with anisotropic displacement parameters. All hydrogen atoms
on organic moieties were treated as idealized contributions.
All scattering factors and anomalous dispersion factors are
contained in the SHEXTL 5.10 program library.21
SiLN is replaced in 2 by an AB quartet (δΗ 6.33, 6.17;
2
J HH ) 3.8 Hz), indicating an unsymmetrical coordina-
tion environment for the silylene ligand within 2. 31P-
{1H} NMR reveals a pair of doublets separated by ca.
80 ppm, with an unprecedentedly large coupling con-
stant for a chelating diphosphine containing a four-
carbon backbone (δ 60.2, -10.3; J PP ) 263 Hz). The
strong P-P coupling implies an unexpected trans
disposition of inequivalent phosphorus atoms, while the
large peak separation indicates the presence of two
different ring sizes. Phosphine ligands within four-
membered chelate rings normally resonate 50-100 ppm
upfield of those in five- and seven-membered chelates
or monodentate phosphines.22 The observed pattern
finds precedent in bis(phosphine) systems in which one
PPh3 ligand is orthometalated to give a four-membered
Ru-P-C-C ring at ∼0 ppm, and a second, trans, PPh3
is a simple η1-donor ligand at a “normal” chemical shift
value of ∼50 ppm.22 The presence of both four- and five-
membered rings in 2 was confirmed by X-ray crystal-
lographic analysis, which reveals an unprecedented
attack of the metal on the four-carbon backbone of the
dcypb ligand. We15 and others23-25 have reported the
high activity of ruthenium cyclohexylphosphine systems
toward attack on saturated C-H bonds under mild
conditions. While intramolecular bond activation typi-
cally involves the cyclohexyl rings, formation of 2 clearly
shows that for diphosphines forming sufficiently flexible
chelate rings attack on the carbon backbone is also
possible. Agostic interactions between Ru and R-meth-
ylene groups of bound Ph2P(CH2)4PPh2 (bis(diphenyl)-
phosphinobutane, dppb) have been described within a
sterically congested bis(dppb) complex, resulting in
deuterium incorporation into the four-carbon backbone
on treatment with D2.26 Interception of the oxidative-
addition product in 2 may result from facile abstraction
of HCl by the basic silylene moiety.
Resu lts a n d Discu ssion
We recently reported a high-yield route to chloride-
bridged ruthenium species 1, a synthetically valuable
source of the RuCl2(dcypb) fragment.15 A suspension of
1 in benzene reacts with SiLN within 4 h at 50 °C,
2
yielding a homogeneous orange solution in which 2 is
the sole Ru-containing product (eq 1). Also evident by
1H NMR analysis is HClSiLN2, identified by comparison
to an authentic sample.
At 185 K, the downfield 31P NMR signal for 2 resolves
into two distinct doublets of approximately equal in-
tensity (δ 62.2, J PP ) 274 Hz; δ 54.3, J PP ) 260 Hz),
while the upfield doublet broadens into two poorly
resolved, overlapping doublets centered at -10 ppm.
The corresponding solid-state spectrum shows only one
of these sets of doublets (δ 56.2, -11.6; J ) 267 Hz; the
<2 ppm chemical shift difference between the solid-state
and low-temperature data is not considered signifi-
cant27). These observations are consistent with a weak
agostic interaction between Ru and a But C-H bond,
observable in the solid state, but favored only at low
temperature in solution. An agostic ν(C-H) band is
found in the solid-state IR spectrum, but not in solution;
X-ray evidence for such an interaction is presented
Use of 1 equiv of silylene results in 50% conversion;
with 2 equiv, quantitative reaction is effected, and 2 can
be isolated as an air-sensitive yellow precipitate in
>80% yield. The same products form more slowly at RT,
and no intermediates are spectroscopically observable.
29Si{1H} NMR analysis of 2 reveals a triplet at 105.7
ppm, supporting identification as a Ru-silylene species
(22) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(23) Chaudret, B.; Dagnac, P.; Labroue, D.; Sabo-Etienne, S. New
J . Chem. 1996, 20, 1137.
(24) Leitner, W.; Six, C. Chem. Ber. 1997, 130, 555.
(25) Six, C.; Gabor, B.; Gorls, H.; Mynott, R.; Philipps, P.; Leitner,
W. Organometallics 1999, 18, 3316.
(26) Ogasawara, M.; Saburi, M. Organometallics 1994, 13, 1911.
(27) Bemi, L.; Clark, H. C.; Davies, J . A.; Fyfe, C. A.; Wasylishen,
R. E. J . Am. Chem. Soc. 1982, 104, 438.
(20) Blessing, R. Acta Crystallogr. 1995, A51, 33.
(21) Sheldrick, G. M. Bruker AXS; Madison, WI, 1997.

Ruthenium Silylene Complex
Sch em e 1
Organometallics, Vol. 21, No. 3, 2002 537
below. An alternative silyl-silylene equilibrium process5
involving reversible migration of chloride ligand to Si
may be discounted on the basis of the near-identity of
the 31P NMR values for the two species.
F igu r e 1. ORTEP diagram of RuCl(η3-dcypb)(SiLN2), 2,
with thermal ellipsoids shown at the 30% probability level.
Hydrogen atoms, solvate molecules, and mirror image
complex omitted for clarity. An ORTEP diagram of the
mirror image complex is included in the Supporting
Information.
Mech a n ism . The observed requirement for 2 equiv
of SiLN per Ru in the synthesis of 2 results from
2
consumption of 1 equiv of the basic silylene ligand as
HClSiLN2, as noted above. Coordination of SiLN as a
2
simple donor ligand (Scheme 1, path A) may generate
sufficient steric pressure to trigger oxidative addition
of a diphosphine C-H bond to the electron-rich metal
center, accompanied by insertion of silylene into the
reported for [Cp*(Me3P)2RudSiMe2][B(C6F5)4].10 π-Bond-
ing between the metal and silicon centers is improbable,
however, as discussed in more detail below.
Ru-Cl bond. Reductive elimination of HClSiLN from
2
Of note in the structure are the Ru-Si-N angles,
which differ by nearly 40°. This difference reflects a 20°
Ru(IV) intermediate A, with coordination of a second
silylene, would afford 2. The Ru(IV) oxidation state is
readily accessible in species containing strongly basic
donor ligands. Examples include Cp*Ru silyl hy-
drides3,9,10,28 as well as alkylphosphine complexes.29,30
Precedent also exists, however, for direct insertion of
“tipping” of the SiLN ligand from an axis drawn from
2
Ru through Si and the centroid of the silylene ring. Like
the 20° deviation from linearity in the Cl-Ru-Si angle,
this distortion minimizes steric interactions between the
But group on N(2) and the cyclohexyl substituents, while
promoting development of the Ru/C-H agostic interac-
tion.
SiLN into a M-Cl bond (path B).5 In view of the bulk
2
of the phosphine and silyl ligands, intermediate B may
be more likely than six-coordinate A. Crystallographic
evidence for four-coordinate Ru within a sterically
encumbered ligand environment was recently reported.31
X-ray quality crystals of 2 were obtained by slow
evaporation of a benzene solution. The complex (Figure
1) exists as two crystallographically equivalent mirror
images. The short nonbonding distance between the Ru
center and a methyl carbon of one of the But groups
(2.899(7) Å) suggests an agostic interaction between the
C-H bond and the Ru center. The solid-state geometry
about the Ru center is thus best described as distorted
octahedral, with the dcypb ligand functioning as an η3-
donor, oriented in a mer fashion with the activated
carbon of the C4 backbone trans to the agostic interac-
tion. The SiLN2 ligand is trans to the remaining chloride
ligand (Si-Ru-Cl ∼160°) and is planar at silicon (sum
of bond angles ) 359.81°, ∼360°). The Ru-Si bond
distance of 2.2264(11) Å is to our knowledge the shortest
known, being slightly less than the value of 2.238(2) Å
F r on tier Or bita l An a lysis. The emerging picture
of the SiLN2 moiety is of a predominantly σ-donor ligand,
in which internal stabilization of the silylene is effected
by donation of electron density from the lone pairs on
nitrogen into the empty Si p orbital.32,33 Consistent with
minimal electronic perturbation of the ligand within 2,
relative to free SiLN2, is the small 29Si NMR coordination
shift. The observed value of δ 106 is well within the δ
97.5-146.9 range described for complexes containing
primarily σ-donor silylenes.2-6,10 Furthermore, despite
the very short Ru-Si bond distance, the bond lengths
within the SiLN2 fragment itself are very slightly shorter
than those of the free silylene.12 Examination of the
frontier molecular orbitals supports this analysis. For
complex 2, assuming an octahedral solid-state geometry,
a dxy, dxz, or dyz orbital must constitute the HOMO.
Ruthenium-silylene back-bonding requires localization
of the HOMO on dxy, and the LUMO on a vacant Si p
orbital (the dxz and dyz orbitals are orthogonal to the Si
p orbital, precluding overlap). Density functional theory
calculations17 carried out on intact 2 suggest that while
the HOMO has the appropriate symmetry, the LUMO
is localized not on Si but on Ru and, in part, on the
Ru-C bond. The HOMO-LUMO gap is approximately
4 eV. The cumulative evidence thus supports identifica-
(28) (a) Djurovich, P. I.; Carroll, P. J .; Berry, D. H. Organometallics
1994, 13, 2551. (b) Wada, H.; Tobita, H.; Ogino, H. Organometallics
1997, 16, 3870. (c) Wada, H.; Tobita, H.; Ogino, H. Organometallics
1997, 16, 2200. (d) Mitchell, G. P.; Tilley, T. D. J . Am. Chem. Soc.
1997, 119, 11236.
(29) Rodriguez, V.; Sabo-Etienne, S.; Chaudret, B.; Thorburn, J .;
Ulrich, S.; Limbach, H.-H.; Eckert, J .; Barthelat, J .-C.; Hussein, K.;
Marsden, C. J . Inorg. Chem. 1998, 37, 3475.
(30) Drouin, S. D.; Yap, G. P. A.; Fogg, D. E. Inorg. Chem. 2000, 39,
5412.
(31) Sanford, M. S.; Henling, L. W.; Day, M. W.; Grubbs, R. H.
Angew. Chem., Int. Ed. 2000, 39, 3451.
(32) Denk, M.; Green, J . C.; Metzler, N.; Wagner, M. J . J . Chem.
Soc., Dalton Trans. 1994, 2405.
(33) West, R.; Denk, M. Pure Appl. Chem. 1996, 68, 785.

538 Organometallics, Vol. 21, No. 3, 2002
Amoroso et al.
Sch em e 2
tion of the silylene ligand as a σ-donor to Ru, the very
short Ru-Si distance likely resulting from the strong
electrostatic interaction between this electrophilic ligand
and the electron-rich metal center.
Rea ction of Silylen e Com p lex w ith Hyd r ogen .
The low reactivity reported for Cp*Ru(SiX2)(PMe3)2]+
(X ) SMe2, Me) toward nonpolar, unsaturated sub-
strates11 and H210 is unsurprising given the coordinative
saturation of the metal in these complexes. Such reac-
tions are of keen interest in view of (1) the possible role
of silylene intermediates in organosilicon transforma-
tions involving evolution or reaction with H2,7 and (2)
the more recent interest in silylene ligands as phosphine
equivalents.2,4 The accessibility of coordinatively un-
saturated 2 affords a means of probing the reactivity of
the silylene ligand toward displacement and/or hydro-
genolysis. Investigations of the reactivity of 2 toward
H2 and CO were thus undertaken.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 2
Reaction of 2 under 1 atm H2 is very slow at room
temperature, with <50% conversion after 1 week, but
can be driven to completion within 24 h at 50 °C. No
intermediates are evident by 31P NMR analysis. The Ru
product is spectroscopically identical (1H and 31P NMR)
to hydridochloro species 4, prepared in independent
work by treating 1 with potassium tri(sec-butyl)boro-
hydride.19 Loss of the silicon ligand is further supported
by X-ray crystallographic analysis of a decomposition
product serendipitously obtained on attempted isolation
of 4 from the reaction mixture (vide infra). 1H, 13C, and
29Si NMR analysis of the sole Si-containing product
permits its identification as [LN2Si(H)]2O 3,18 suggesting
that reaction involves both hydrogenolysis and, more
unexpectedly, hydrolysis. (The latter may occur, despite
the use of standard “anhydrous” Schlenk techniques,
from use of a Deoxo cartridge to scavenge trace oxygen
from the H2 stream by catalytic conversion to water; no
evidence of hydrolysis was observed under N2 atmo-
sphere.) Implication of water in this transformation is
confirmed by complete conversion of 2 to 4 and siloxane
3, without heating, on addition of stoichiometric quanti-
ties of H2O under H2. Other side-products form on use
of water alone; these are partially converted to 4 and
siloxane on subsequent exposure to H2. Reaction with
both water and H2 is thus required to generate the
observed hydride and siloxane products. The overall
reaction of 2 is indicated in eq 2.
empirical formula
fw
temperature
wavelength
cryst syst, space group
unit cell dimens
C44H77ClN2P2RuSi
860.63
203(2) K
0.71073 Å
monoclinic, Pc
a ) 13.503(1) Å, R ) 90°
b ) 17.697(2) Å, â ) 105.742(2)°
c ) 20.110(2) Å, γ ) 90°
4625.3(8) Å3
volume
Z, calcd density
abs coeff
F(000)
cryst size
4, 1.236 mg/m3
0.522 mm-1
1840
0.2 × 0.2 × 0.1 mm
θ range for data collection
limiting indices
1.15-28.83°
-17 e h e 18, 0 e k e 23,
-26 e l e 25
no. of reflns collected/unique
completeness to θ ) 28.83
abs corr
max. and min. transmn
refinement method
36492/17571 [R(int) ) 0.0496]
92.3%
semiempirical from equivalents
0.928076 and 0.613589
full-matrix least-squares on F2
no. of data/restraints/params 17571/2/895
goodness-of-fit on F2
1.021
0.0388
0.0513
Ra
Rw
b
a
b
2 1/2
R ) ∑||Fo| - |Fc||/∑||Fo|. Rw ) [∑wδ2/∑wFo
] .
of the product mixture reveals one 29Si resonance (δ
-57.6), confirming identification of this species as
siloxane dimer [LN2Si(H)]2O 3.18
J utzi and co-workers recently described the synthesis
of metallosilanol species Cp2Mo(H)(SiLN2OH), via con-
trolled hydrolysis of Cp2Mo(SiLN2).6 An analogous silyl
hydride complex, Cp2Mo(H)(SiHLN2), was obtained by
insertion of SiLN into an M-H bond of Cp2MH2 (M )
2
Mo, W).6 Interestingly, 2 appears to be stable toward
hydrogenolysis alone, despite the presence of the Ru-C
and silylene entities and the coordinative unsaturation
of the metal. Thus, we see no products that can be
attributed to reaction with H2 alone: while this might
in principle be accounted for by a (2 + H2) equilibrium
that lies far to the left, reaction with D2 would then be
expected to effect incorporation of D into the dcypb
backbone (via reductive elimination of the activated
C-H bond). However, labeling studies carried out with
The silylene-siloxane transformation is indicated by
replacement of the olefinic doublets for 2 by two new
signals in the olefinic/silyl region. A singlet at 5.95 ppm
is assigned to a silyl proton on the basis of its correlation
1
with the 29Si peak (1H-29Si HMQC; J SiH ) 278 Hz),
supported by the absence of an H-C correlation in the
corresponding 1H-13C HMQC experiment. Also evident
in this region (5.80 ppm) is one olefinic signal, which at
500 MHz is resolved into a doublet with long-range
2
D2 show no H aliphatic signals prior to emergence of
31P NMR signals for 4-d . In conjunction with the
stoichiometric reactions with H2O/H2 described above,
this implies that reaction of 2 with water precedes
reaction with D2 (or H2). 2H NMR analysis indicates that
1
coupling to silicon (J SiH ) 2 Hz; H/29Si HMBC). This
resonance correlates with a 13C methine signal at δ
111.8, itself assigned by 13C DEPT. 29Si INEPT analysis

Ruthenium Silylene Complex
Organometallics, Vol. 21, No. 3, 2002 539
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for 2a
Ru(1)-Si(1)
Ru(1)-C(14)
Ru(1)-P(2)
Ru(1)-P(1)
Ru(1)-Cl(1)
2.2264(11), 2.2293(12)
2.110(4), 2.114(4)
2.3373(12), 2.3279(12)
2.3389(12), 2.3422(11)
2.4713(11), 2.4738(10)
Si(1)-N(1)
Si(1)-N(2)
N(1)-C(33)
N(2)-C(34)
C(33)-C(34)
1.732(3), 1.725(3)
1.734(3), 1.741(3)
1.388(5), 1.377(6)
1.399(6), 1.411(6)
1.336(6), 1.329(6)
N(1)-Si(1)-N(2)
N(1)-Si(1)-Ru(1)
N(2)-Si(1)-Ru(1)
P(2)-Ru(1)-P(1)
90.60(17), 90.61(17)
116.06(12),116.42(12)
153.15(13), 152.97(13)
152.11(4), 152.91(4)
C(14)-Ru(1)-Si(1)
C(14)-Ru(1)-P(1)
C(14)-Ru(1)-P(2)
C(14)-Ru(1)-Cl(1)
104.45(12), 103.76(12)
69.21(13), 69.50(12)
83.05(13), 83.68(12)
95.16(12), 95.87(12)
a
The second value is the corresponding value for the mirror image complex.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 5
empirical formula
fw
C62H109Cl3N2P4Ru2
1314.88
temperature
203(2) K
wavelength
0.71073 Å
cryst syst, space group
unit cell dimens
triclinic, P1h
a ) 11.6220(9) Å, R ) 89.7230(10)°
b ) 13.5699(10) Å, â ) 86.8370(10)°
c ) 22.7781(17) Å, γ ) 66.5080(10)°
3289.0(4) Å3
volumel
Z, calcd density
abs coeff
2, 1.328 mg/m3
0.716 mm-1
F(000)
1388
cryst size
0.20 × 0.10 × 0.05 mm
θ range for data collection 1.64-28.71°
limiting indices
-15 e h e 15, -17 e k e 17,
0 e l e 30
no. of reflns collected/
unique
25795/14910 [R(int) ) 0.0404]
completeness to θ ) 28.71 87.6%
abs corr
semiempirical from equivalents
max. and min. transmn
refinement method
no. of data/restraints/
params
0.928076 and 0.828149
full-matrix least-squares on F2
14 910/0/658
goodness-of-fit on F2
Ra
1.028
0.0487
0.0971
b
Rw
F igu r e 2. ORTEP diagram of [(dcypb)(H)Ru(µ-Cl)3Ru-
(dcypb)(N2)], 5, with thermal ellipsoids shown at the 30%
probability level. Hydrogen atoms and solvate molecule
omitted for clarity. Line diagram shows position of hydride
(not located crystallographically).
a
b
2 1/2
R ) ∑||Fo| - |Fc||/∑||Fo|. Rw ) [∑wδ2/ ∑wFo
] .
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
N(1)-N(2)
Ru(1)-N(1)
Ru(1)-P(1)
Ru(1)-P(2)
Ru(2)-P(3)
Ru(2)-P(4)
1.110(5)
1.898(6)
2.3225(11)
2.3369(11)
2.2352(11)
2.2419(12)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Cl(3)
Ru(2)-Cl(1)
Ru(2)-Cl(2)
Ru(2)-Cl(3)
2.4840(10)
2.4793(10)
2.4636(10)
2.6092(10)
2.5403(10)
2.5107(11)
the siloxane product formed in these reactions, whether
at RT or by thermolyis, is solely [LN2Si(D)]2O. Consistent
with these observations is the mechanism of Scheme 2,
in which evolution of siloxane results from successive
reaction of 2 with H2O and D2 (H2). Nucleophilic attack
of water on bound silylene may afford a η1-silanol
hydride intermediate,6 which reductively eliminates to
yield a silanol species containing a simple η2-diphos-
N(2)-N(1)-Ru(1) 173.0(4)
P(3)-Ru(2)-P(4)
96.67(4)
N(1)-Ru(1)-P(1)
N(1)-Ru(1)-P(2)
P(1)-Ru(1)-P(2)
92.46(13) Ru(1)-Cl(1)-Ru(2) 83.41(3)
94.82(12) Ru(1)-Cl(2)-Ru(2) 84.95(3)
93.46(4)
Ru(1)-Cl(3)-Ru(2) 85.91(3)
phine ligand. Reaction with H2 would then liberate LN
-
2
SiD(OH) (which can then condense to form the siloxane
318) and a hydride species. Dimerization of the latter
and reaction with D2 would give 4. Not indicated in
Scheme 2 are miscellaneous reactions involving scram-
bling of the deuterium label into the Cy rings and/or
dcypb backbone. Exchange of Ru-D into phosphine
cyclohexyl C-H bonds is common,15,23-25 while exchange
with C4-methylene backbones in a dppb complex26 was
noted above.
Cr ysta l Str u ctu r e of 5. We recently described the
susceptibility of the parent dcypb complex 1 to intramo-
lecular dehydrogenation on removal of H2 atmosphere
or concentration to dryness.15 Dehydrogenation likewise
results from attempted isolation of 4, as indicated by
the emergence of olefinic signals and a singlet for
dissolved H2. Such processes may thus be a general
characteristic of Ru-dcypb complexes in coordinatively
unsaturated environments. That other, intermolecular,
processes are involved, at least in decomposition of 4,
is suggested by the presence of an additional chloride
ligand in [(dcypb)(H)Ru(µ-Cl)3Ru(dcypb)(N2)] 5. The
latter species, identified by X-ray crystallography, crys-
tallized on attempted isolation of 4 following reaction
of 2 with H2/H2O. A benzene solution containing the
products was stripped to dryness, and the residue was
washed with a few drops of hexanes, then redissolved
in benzene. Crystals of 5 deposited on slow evaporation
under N2. Many other species are also present in
solution, as judged by 31P and 1H NMR. An ORTEP
representation of 5 (accompanied by a line drawing)
appears in Figure 2, with crystallographic and selected
structural parameters in Tables 3 and 4, respectively.

540 Organometallics, Vol. 21, No. 3, 2002
Amoroso et al.
Complex 5 adopts a triply chloride-bridged diruthe-
nium structure, in which the coordination geometry at
each metal center is distorted octahedral, taking into
consideration the presence of a hydride ligand on Ru-
(2). The structure is unsymmetrical, with Ru(1) bearing
an end-bound dinitrogen ligand. Location of the hydride
ligand on Ru(2) is inferred from the very long Ru(2)-
Cl(1) bond distance (2.6092(10) Å, vs the average Ru-
Cl bond length of 2.496(10) Å). The presence of this
sterically undemanding ligand permits a larger bite
angle of the diphosphine ligand subtended at Ru(2), vs
1
the more sterically crowded Ru(1) (96.7°, vs 93.5°). H
NMR analysis of the isolated solid shows several hy-
dridic resonances. While a search of the Cambridge
Crystallographic Database reveals no direct analogues
of the “Ru(µ-Cl)3Ru(H)” framework, the structural pa-
rameters for 5 are very similar to data reported for the
closely related complex [(η2-H2)(dppb)Ru(µ-Cl)3RuCl-
(dppb)].34 Ruthenium-phosphorus, -nitrogen, and -chlo-
ride distances (other than for the chloride trans to
hydride) tally closely with the values reported, as do
angles within the Ru-P-Cl skeleton.
between the meridional extreme of 6/7 and a true facial
arrangement, is thus suggested.
Con clu sion s
The foregoing describes an unusual example of a
silylene moiety found within a coordinatively unsatur-
ated ligand environment containing chloride and phos-
phine ligands, in which a novel η3-coordination mode
for the chelating diphosphine results from activation of
an sp3 C-H bond within the tetramethylene backbone.
Solid-state and low-temperature NMR data, supported
by crystallographic analysis, suggest a coordinatively
saturated structure, in which an agostic interaction
occupies the sixth coordination site. Confirmation of the
accessibility of this site in solution, and indications of
the noninnocent behavior of the silylene ligand, comes
from the observed reactivity toward both H2/H2O and
CO. Displacement of silylene by CO is facile at room
temperature, giving access to novel η3-dcypb carbonyl
complexes. Hydrolysis and hydrogenolysis afford a
simple η2-dcypb complex, with elimination of bound
silylene as siloxane. These results join several recent
examples in suggesting thatsin contrast to current
views of the analogous, Arduengo-type carbenessthe
Rea ction w ith Ca r bon Mon oxid e. Suspensions of
2 react with CO within hours to give a clear pale yellow
solution containing free SiLN and three isomeric ru-
2
thenium carbonyl derivatives, 6-8. The high solubility
of the Ru products hampered their separation from each
other and from free silylene. Displacement of SiLN is
2
indicated by the complete disappearance of the 1H NMR
AB quartet for the bound ligand and emergence of a
prominent singlet for free silylene (6.75 ppm). Retention
of the η3-dcypb framework in 6-8 is indicated by the
characteristically large 31P{1H} NMR peak separations
(∆δP ∼100 ppm). Unambiguous identification of all three
as isomeric bis(CO) derivatives (eq 3) is provided by 31
P
NMR analysis of their 13CO isotopomers. 31P-13C split-
ting results in transformation of each doublet present
in the original 31P NMR spectrum into a doublet of
doublets of doublets (6, 7) or a doublet of triplets (8).
Isomers 6 and 7 contain trans-disposed phosphorus
SiLN ligand can readily participate in reactions at
2
transition-metal metal centers.
2
ligands, as indicated by their large J PP values (∼250
Hz). Distortion from the idealized structures repre-
sented in eq 3 is indicated by the observation of four
inequivalent 13CO resonances for 6 + 7 (as well as two
for 8). Consequently, 6 and 7 cannot be distinguished
by spectroscopic data.
Ack n ow led gm en t. Helpful discussions with Profes-
sor Michael Denk (Toronto) are acknowledged with
thanks. This work was supported by the Natural Sci-
ences and Engineering Research Council of Canada, the
Canada Foundation for Innovation, and the Ontario
Innovation Trust.
A structural distinction between these products and
2
isomer 8 is indicated by the much smaller J PP value
for the latter (164 Hz), which implies a smaller P-Ru-P
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data collection and refinement parameters, atomic coordinates,
bond lengths and angles, anisotropic displacement parameters,
and hydrogen coordinates for 2 (and its mirror image complex)
and 5. An ORTEP diagram for the mirror image of 2 is also
included. This material is available free of charge via the
Internet at http://pubs.acs.org.
dihedral angle. That the angle is still much larger than
90° is indicated, however, by comparison of this coupling
2
constant to “normal” cis J PP values of 11-50 Hz.22
A
highly distorted octahedral arrangement, with the
diphosphine ligand taking up a geometry intermediate
(34) MacFarlane, K. S.; Thorburn, I. S.; Cyr, P. W.; Chau, D. E. K.
Y.; Rettig, S. J .; J ames, B. R. Inorg. Chim. Acta 1998, 270, 130-144.
OM0101801